The present invention relates generally to wireless networks and more specifically to a protocol between infrastructure nodes and wireless clients to enhance the operation of a High Density Wireless Local Area Network (HD WLAN).
The IEEE 802.11 Standard is well established and provides the Physical Layer (PHY) and Medium Access Control Layer (MAC) specifications for fixed, portable, and moving stations requiring wireless connectivity within a local area. Included in the Standard are several PHY radio parameters that help define the radio frequency (RF) range of a BSS (cell). Included within these parameters are Transmit Power, Receive Sensitivity, and Clear Channel Assessment (CCA). The Standard specifies these parameters (partly) in order to provide unbiased wireless network access privileges to all user stations.
The CCA requirement defined in the Standard (part of the Carrier Sense Medium Access and Collision Avoidance (CSMA/CA) protocol) requires each station with an impending transmission to sense the medium (airwaves) and determine if the medium is busy first in order to avoid a collision with another station transmission. The Standard further specifies that compliant stations are capable of setting the receiver energy detect threshold used in accordance with the CCA requirement at a level approximately at or below the receiver's minimum sensitivity level (see IEEE 802.11 specifications for details) when verifying conformance. Importantly, with respect to station transmit power, the Standard also specifies that the energy detect threshold, as part of the CCA, may be adjusted higher for lower transmit power levels.
In a typical IEEE 802.11 network, the minimum cell size that may be realized is closely related to the transmit power output (minimum) and the receiver sensitivity (rate dependent). A typical adjustment range for WLAN stations may be about 1 mW to 100 mW (0 dBm/20 dBm) while typical receiver sensitivities are normally fixed (not adjustable) slightly below the minimum specified Standard requirement for compliance. Although reducing the transmit power even lower (than 1 mW) may seem a reasonable approach to reducing (configurable) cell sizes even further, radio development issues may become critical (which are outside the scope of this application) and therefore, this cell size adjustment means may be considered undesirable.
In larger multi-cell wireless networks where RF channel frequency reuse is common, a minimum percentage of inter-cell overlap is usually desirable in order to minimize RF channel contention. Then, an increase in the multi-cell density for such larger networks effectively worsens the RF channel contention problem as a result of the increased number of co-channel (contending) stations present and the excessive inter-cell coverage overlap that occurs. A method to mitigate the inter-cell contention problem in high density networks may be accomplished by means of adjustment of the AP and client station receiver sensitivity, CCA sensitivity, and transmit power output parameters in a relatively cooperative manner. As a result, the RF channel capacity may be optimized and an overall WLAN capacity performance increase may be realized. Thus, a need exists for a technique to control the adjustment of the AP and client station receiver sensitivity, CCA sensitivity, and transmit power output parameters in a relatively cooperative manner.